1. Field of the Invention
The present invention relates to an energy-dispersive-type semiconductor x-ray detector (hereinafter called the EDS detector) used for energy-dispersive-type element analyzers, for example, such as x-ray microanalyzers which are combined with an electron microscope and measure characteristic x-rays excited with an electron beam and emitted from a specimen, and fluorescence x-ray analyzers using x-ray excitation, and more particularly to an EDS detector in which a small-sized gas-circulation-type refrigerator is provided in a cryostat sliding in a given direction, helium gas is supplied through a connecting pipe to the refrigerator, and an x-ray detecting element is cooled by means of the refrigerator.
2. Description of Related Art
Although heretofore, as an EDS detector used for energy-dispersive-type element analyzers requiring a high resolution, lithium-drift-type silicon semiconductor x-ray detectors (silicon lithium detectors) have been widely used, the silicon (lithium) detectors have a problem in that when a drifted lithium ion moves into silicon due to thermal diffusion, the characteristics of the x-ray detecting element deteriorates, so that the element must be cooled by the use of liquid nitrogen at all times and liquid nitrogen replenished, thereby making daily maintenance troublesome.
On the other hand, as an alternative to the above-mentioned liquid nitrogen system, a small-sized gas-circulation-type refrigerator such as of a Joule-Thomson system and of pulse tube system has been developed. The small-sized gas-circulation-type refrigerator has a sufficient refrigerating capacity, has no mechanically driving part in the low-temperature generating section, and is simple in construction, so that the refrigerator is characterized by an extremely low vibration, a high reliability with respect to long-time operation, and an easy maintenance. There has been attempts to provide a small-sized gas-circulation-type refrigerator in a cryostat sliding in a given direction, to supply helium gas through a connecting pipe to the above-mentioned refrigerator, and to cool an x-ray detecting element by means of the above-mentioned refrigerator.
FIG. 4 shows schematically the configuration of a prior art EDS detector 40, in which numeral 41 designates a cryostat configured so as to be slid on a guide base 42 in the arrow F or R direction. Provided in the cryostat 41 is a pulse tube refrigerator 43, which includes a cold heat exchanger portion 43b and a refrigerator body 43a which is connected to a cold finger 44 extending in the horizontal direction. Provided on the head of the cold finger 44 is an x-ray detecting element 45. Numeral 46 designates an x-ray window provided in front of the x-ray detecting element 45.
The refrigerator body 43a of the above-mentioned pulse tube refrigerator 43 is connected through a connecting pipe 47 to a pressure converting valve unit 48, which, in turn, is connected through a high-pressure helium piping 49 and a low-pressure helium piping 50 to a compressor 51. Numeral 47a is a flexible pipe portion of the connecting pipe 47 connected to the refrigerator body 43a.
In the EDS detector 40 having the above-mentioned configuration, the high-pressure and low-pressure helium gases adjusted by the compressor 51 are supplied to the pressure changeover valve unit 48, and the pressure wave of the above-mentioned helium gas is supplied through the connecting pipe 47 to the refrigerator body 43b of the pulse tube refrigerator 43, whereby the refrigerator body 43a is acceleratedly cooled, and due to the cold generated, the cold finger 44 is cooled and thus the x-ray detecting element 45 is cooled.
However, in this case, the above-mentioned connecting pipe 47 may vibrate due to the pressure wave of the helium gas therein, so that the vibration is transferred to the cryostat 41 housing the x-ray detecting element 45, whereby the x-ray detecting element 45 may be vibrated or an electron microscope to which the EDS detector 40 is mounted may be vibrated, which can adversely affect the accuracy in measurement and in x-ray detection.
Accordingly, the prior art is still seeking improvements in this field.